Tissue repair device and fabrication thereof

ABSTRACT

A device for use in tissue repair, a method of using the device in a surgical procedure and a method of making the device. The device is an assembly of a anchor with a cord passed through it, and a stopper to prevent the cord from passing back through the anchor.

FIELD OF THE INVENTION

The present invention relates to medical devices. More specificallymedical devices for use in tissue repair, surgical procedures forrepairing tissue using such devices, and a method of making the devices.

BACKGROUND OF THE INVENTION

There are many applications in the field of orthopaedics for medicaldevices used in surgical procedures, wherein there is a requirement toanchor at least a section of a cord (e.g., a tape or a surgical suture)within a bone bore hole. A solid and secure attachment between the cordand anchoring components of anchor devices is essential to the successof the device. Such conventional devices include vertebral straps,suture anchors, and suture staples.

Conventionally known methods for attaching or securing cords toanchoring components include insert molding, passing the cords througheyelets or small holes in the anchoring components, compressing the cordbetween surfaces of the device, etc. Although generally satisfactory fortheir intended purpose, there may be certain disadvantages attendantwith the use of such attachment methods. For example, a disadvantage ofthe insert molding method may be low pull-out strength of the cord fromthe anchoring component. This is believed to be caused by the difficultyin general, conventional compression molding processes to form a secureattachment between the cord and anchoring components. When using aneyelet or small hole, the hole or the eyelet are related to the removalor absence of material from the anchoring component which may, in somecases, result in mechanical strength lost, or it may be difficult or notpossible to place a hole or an eyelet in or on the anchoring componentdue to a low profile configuration or limited space.

Accordingly, there is a need in this art for novel medical devices foruse in tissue fixation, wherein the devices have a flexible cordattached.

SUMMARY OF THE INVENTION

The tissue repair device of the present invention overcomes the abovestated limitations by providing a device having a cannulated anchormember, a cord that passes through the anchor cannulation, a rod member,and a stopper to prevent the cord from passing back through the anchorcannulation, wherein the rod member is passed through and end of thecord and imbedded within the stopper. The stopper member is molded aboutthe cord end containing the rod member. This enhances the attachmentstrength of the cord to the stopper.

Another aspect of the present invention is a method of using thepreviously-described device in a surgical procedure.

Yet another aspect of the present invention is a method of manufacturingthe tissue repair devices of the present invention.

The novel tissue repair devices having cannulated anchor members, cordsand stopper members overcome the disadvantages of the prior art byproviding secure fixation and minimizing or eliminating the possibilityof the cord separating from the anchor member.

These and other features and advantages of the present invention willbecome more apparent from the following description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an embodiment of a tissue repair device of thepresent invention.

FIG. 2 a is a cross-sectional view of the device of FIG. 1.

FIG. 2 b is a cross-sectional view of the device of FIG. 1 rotated 90°.

FIG. 3 is a detailed cross-sectional view of a schematic of a moldingassembly for forming the stopper assembly of the device of the presentinvention.

FIG. 4 a illustrates molding assembly of FIG. 3 at the onset of themolding process.

FIG. 4 b illustrates the molding assembly of FIG. 4 a at the conclusionof the molding process.

FIG. 5 is a cross-sectional view of a device that has a second anchormember with a first and a second stopper member mounted to the cord inthe same manner as the tissue repair device of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The tissue repair device of the present invention is a device that has acannulated anchor member through which a cord passes, and a stopper thatprevents the cord from passing back through the anchor. The stopper ismolded around an end of the cord and a rod is passed through the cordand imbedded within the stopper. This enhances the attachment strengthof the cord to the stopper.

An embodiment of the device 10 of the present invention is seen in FIGS.1 and 2. Device 10 is seen to have a cannulated anchor member 20, a cord40, a rod member 60 and a stopper 50. Anchor member 20 has first end 21and second end 22, and outer surface 23. A plurality of ridge members 24are seen to extend out from anchor member 20 to assist in securing theanchor member 20 in tissue. If desired, other types of conventionaltissue securement members may be utilized including screw threads,spikes, projections having various geometric configurations such aspyramidal, cylindrical, hemispherical, etc. Anchor member 20 is alsoseen to have longitudinal passage 30 extending therethrough and to alsohave opening 31 in first end 21 and opening 32 in second end 22, bothopenings are in communication with passage 30. Longitudinal passage 30may have a variety of cross-sections including circular, square,rectangular, oval and the like. Cord 40 is seen to be an elongatedflexible member, preferably made from a plurality of fibers although acord made from a single element may be used. Examples of cords 40 thatmay be used in the devices 10 of the present invention includeconventional sutures, tapes, ropes, and the like. Cord 40 is seen tohave first end 41 and second end 42.

As shown in FIGS. 2 a and 2 b, rod member 60 is embedded in cord 40, andwithin stopper 50. Rod 60 has dimensions d₄ and d₅ where dimension d₄ islarger than dimension d₁ of cord 40 so that rod 60 passes completelythrough cord 40. Stopper member or stopper 50 is seen to be asubstantially disc-like member having top 51, bottom 52 and side 54. Thestopper member 50 may have a variety of geometric configurationincluding spheres, cubes, cylinders, pyramids, and combinations thereofand the like. As mentioned previously above, anchor member 20 iscannulated and has longitudinal passage 30. The maximum dimension of thecross-section of passage 30 has dimension d₂ that is sufficient for thethrough passage of cord 40 (with dimension d₁) through anchor member 20.Stopper member 50 has outer dimension d₃ sufficiently greater than d₂ toeffectively prevent it from passing through longitudinal passage 30 ofanchor member 20.

Cord 40 is composed of fibers, and may be in any of the forms known intextile technologies. These forms include braids, weaves, and knits. Ifbraided, cord 40 can be in the form of a biaxial, triaxial, or tailoredbraid, or a braid formed by other known braiding methods. Cord 40 mayalso consist of a single element, e.g., a strip cut from a polymericfilm, etc.

Rod 60 is seen to be a substantially cylindrical member having opposedends 61 and 62 and outer surface 65. Although shown as having acylindrical geometry, with a circular cross-section, rod member 60 mayhave other geometries (triangular, square, rectangular, ovalcross-sections} that will function in a similar manner. In addition, ifdesired, although not shown, the ends 61 and 62 may be rounded orpointed.

Suitable materials from which cannulated anchoring member 20, cord 40and rod 60 may be formed include biocompatible polymers selected fromthe group consisting of aliphatic polyesters, polyorthoesters,polyanhydrides, polycarbonates, polyurethanes, polyamides andpolyalkylene oxides. They also can be formed from biocompatible metals,glasses or ceramics, or from autograft, allograft, or xenograft bonetissues.

Anchoring member 20, cord 40, and rod 60 further can be made from orinclude combinations of metals, ceramics, glasses and polymers.

The biocompatible materials can be biodegradable or non-biodegradable.Biodegradable materials, such as polymers, readily break down into smallsegments when exposed to moist body tissue. The segments then either areabsorbed by the body, or passed by the body. More particularly, thebiodegraded segments do not elicit permanent chronic foreign bodyreaction, because they are absorbed by the body or passed from the body,such that no permanent trace or residual of the segment is retained bythe body.

In one embodiment, cannulated anchor member 20, cord 40, or rod 60 aremade from biodegradable aliphatic polymer and copolymer polyesters andblends thereof. The aliphatic polyesters are typically synthesized in aring opening polymerization. Suitable monomers include but are notlimited to lactic acid, lactide (including L-, D-, meso and D,Lmixtures), glycolic acid, glycolide, epsilon-caprolactone, p-dioxanone(1,4-dioxan-2-one), and trimethylene carbonate (1,3-dioxan-2-one).

Several preferred materials for anchor member 20, cord 40, and rod 60include poly(lactic acid), or PLA, and a copolymer of lactic acid withglycolic acid, or poly(lactide-co-glycolide) (PLGA), in a mole ratio of95 lactic acid to 5 glycolic acid.

In another embodiment, the materials used to make anchor member 20, cord40, or rod member 60 will be biodegradable glasses or ceramicscomprising mono-, di-, tri-, alpha-tri-, beta-tri-, and tetra-calciumphosphate, hydroxyapatite, calcium sulfates, calcium oxides, calciumcarbonates, magnesium calcium phosphates, phospate glasses, bioglasses,and mixtures thereof.

In yet another embodiment, the materials used to make anchor member 20or rod member 60 can be combinations of biodegradable ceramics andpolymers. Composites are prepared by incorporating biodegradable ceramicreinforcements such as particles in a biodegradable polymer matrix.

Stopper member 50 is dimensioned (d₃) so that it will not pass throughpassage 30 dimension d₂ of anchoring component 20. Suitable materialsfrom which stopper member 50 may be formed include the biocompatible andbiodegradable polymers mentioned above. As with anchor member 20,stopper 50 may be made from combinations of biodegradable ceramics andpolymers, or a polymer reinforced with another polymer, such as ashort-fiber polymer reinforcing a polymer matrix. The materials used toform stopper 50 must be flowable, so that they may infiltrate andsurround fibers 45 of end 42 of cord 30. Preferred materials includethermoplastic biocompatible and biodegradable polymers.

One preferred material for stopper 50 is a copolymer ofepsilon-caprolactone with p-dioxanone, orpoly(epsilon-caprolactone-co-p-dioxanone), in a mole ratio of 95epsilon-caprolactone to 5 p-dioxanone.

Anchor member 20 and rod member 60 can be formed by a variety of known,conventional processes. If, for example, these components are made frompolymeric materials, they can be formed by extrusion, injection molding,machining, and the like. They may be treated before being assembled forenhanced mechanical properties. One example of such treatments isannealing. Strength is enhanced by increased crystallinity throughannealing.

As shown in FIGS. 2 a and 2 b, rod 60 is passed through the end 42 ofcord 40 and imbedded within stopper 50. The imbedding of cord 40 and rod60 within stopper 50 occurs during the forming of stopper 40 so thatstopper 50 is molded about the end 42 of cord 40 and rod member 60.

In a preferred embodiment of the present invention, rod member 60 ispassed through one end 42 of cord 40, and both are encapsulated in athermoplastic polymer via a compression molding process as describedherein. In this case, stopper 50 is formed of a thermoplastic polymerthat has a lower melting point than the materials that comprise cord 40and rod 60.

One method of fabricating assembled device 10 of the present inventionis schematically shown in FIGS. 3 and 4. In this embodiment, compressionmolding die assembly 70 is utilized. Die assembly 70 is seen to includea mold 80 having a main cavity 84.

In one embodiment of the fabrication process, rod member 60 is passedthrough end 42 of cord 40. The end of 42 of cord 40 having rod 60disposed therethourgh is disposed in main cavity 84 of die assembly 70.

Next, as shown in FIG. 4 a, a prefabricated polymer tube 90, comprisedof the polymer that will be used to form stopper 50, is disposed in maincavity 84 of die assembly 70 so that it surrounds the end 42 of cord 40having the rod 60 disposed therethrough. The tube 90 is prefabricatedusing extrusion or injection molding or other conventional processes.Conventional plunger 100 is then disposed in main cavity 84 of mold 80of die assembly 50 as shown.

The entire assembly is then heated to a temperature sufficient to meltprefabricated polymer tube 90. As mentioned previously, polymer tube 90must be formed of a thermoplastic polymer that has a lower melting pointthan the materials that comprise rod 60 or cord 40.

Next, plunger 100 is moved in cavity 84 in the direction of cord 40using a conventional injection molding mechanism driven by an electricmotor. The movement of plunger 100 axially in main cavity 84 forces themelted polymer that was tube 90 to flow and embed the rod member 60/cordend 42 combination, and to simultaneously form stopper member 50.

The assembly is cooled, and melted polymer solidifies. After removalfrom mold 80, the solidified polymer rod 60/cord end 42 combination istrimmed to yield the rod 60/cord end 42/stopper 50 assembly used in thetissue anchoring devices of the present invention.

The attachment strength of cord 40 to stopper 50 in the rod 60/cord end42/stopper 50 assembly produced according to the present invention islargely enhanced.

The device 10 is assembled by inserting end 41 of cord 40 into opening31 in end 21 of anchor member 20, and threading cord 40 through passage30 so that end 41 and a section of cord 40 exit out from opening 32 ofend 22.

In another embodiment of the tissue repair devices of the presentinvention shown in FIG. 5, device 110 will have an anchor member 120mounted to each end of the cord 140 in a similar manner with rods 160 ineach end 141 and 142 in stopper members 150 mounted to ends 141 and 142.

The tissue repair devices of the present invention can be used to repaira variety of tissues in various surgical procedures. The devices can beused to approximate tissue, e.g., vertebral repair, approximation ofsoft tissue to the surface of a bone, etc. Those skilled in this artwill appreciate that the anchors of the present invention may also beused with other types of procedures and tissues. The devices may be usedin various tissue repair procedures including rotator cuff repair,spinal repair procedures, etc.

The following example is illustrative of the principles and practice ofthis invention, although not limited thereto.

EXAMPLE 1 Forming Rod/Cord/Stopper Assemblies

In this example, a general compression molding process was used to formrod 60/cord 40/stopper 50 assembly.

The rod 60 was formed by extruding 95/5 poly(lactide-co-glycolide) (95/5PLGA) from PURAC (Gorinchem, The Netherlands), with an InherentViscosity (I.V) of 2.33 dl/gm (measured in chloroform at 25° C. and aconcentration of 0.1 gm/dl) at 200° C. in a DACA Spinline extrusionsystem. The diameter of rod 60 was 0.635 millimeter. Rod 60 was cut to0.4 centimeters in length.

The material used to form stopper 50 was 95/5poly(epsilon-caprolactone-co-p-dioxanone) with an Inherent Viscosity(I.V) of 1.5 dl/gm (measured in chloroform at 25° C. and a concentrationof 0.1 gm/dl). The 95/5 poly(epsilon-caprolactone-co-p-dioxanone) wasprefabricated into a short tube with dimensions of: OD 0.38 centimeters,ID 0.23 centimeters, and 0.30 centimeters long (by extrusion under anextrusion temperature of 85° C.).

The cord was a three dimensional woven cord made using 95/5poly(lactide-co-glycolide) (95/5 PLGA) fibers. The fibers are sold underthe tradename PANACRYL, (Ethicon, Inc., Somerville, N.J.). The cord was3D woven with 100 Denier fiber and a diameter of 2 millimeter at FiberConcepts, Inc. (Conshohocken, Pa.).

Anchor member 20 was made using 95/5 poly(lactide-co-glycolide) byinjection molding billets of the material, and machining them intoanchors.

The rod was passed through the end of the cord and the assembly wasplaced into the mold cavity. The prefabricated short tube was placedinto the mold so that the end of the cord and the rod were inside thetube. The plunger was then put in place, and the mold was closed andplaced into a compression molder (Model 2696, Carver, Inc., Wabash,Ind.). The mold was heated to a temperature of 65° C. for 3 minutes. Theplunger was then moved in the direction of the cord and the mold wascooled to a temperature of 25° C. for 3 minutes under compressionpressure.

As a control, the same procedure was used with the exception that no rodwas passed through the end of the cord. So, in the control there was norod.

The pullout strength of the two assemblies was tested. Pullout testswere performed using an Instron 4501 test frame. The cord was firstloaded on a polyurethane foam block with a pre-drilled hole withdiameter of 2.68 mm, which was fixed in place by a special clamp thatallows movement in the X-Y plane but not the Z (pulling) direction. Thecord end was held tightly by the grips and then a tensile testingprocedure was performed with a cross-head rate of 0.1 millimeter/second.The pullout strength of the control was 18 pounds-force (lbf), whilethat of the assembly with the rod was 32 pounds-force (lbf).

EXAMPLE 2 Surgical Procedure

A patient is prepared for spinal fusion surgery in a conventionalmanner. The surgery will fuse one or more levels of the spinal column.The patient is anesthetized in a conventional manner. The tissue repairsite is accessed by making an incision through the abdominal cavity anddissecting down to the spinal column. A sterile device of the presentinvention is prepared for implantation into the patient, the devicehaving anchor members mounted to each end of the cord. The operativesite is prepared to receive the anchor members of the repair device bydissecting through the ligamentous structure attached to the vertebralbodies of the spinal column that will be fused. A discectomy procedureis performed to remove the disc of the vertebral level to be fused and abone graft is inserted into the discs space. A hole is drilled into thevertebral body above and below the disc space. The anchor bodies arethen inserted into drilled holes in the adjoining vertebrae to be fused.The cord of the device is used to prevent migration of the bone graft inorder to complete the tissue repair. The incision is approximated in aconventional manner using conventional surgical sutures. The incision isbandaged in a conventional manner, thereby completing the surgicalprocedure.

The novel devices and method of the present invention provide thepatient and surgeon with multiple advantages. The advantages includeincreased pull-out strength and a decoupling of the anchor member fromthe cord.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

1. A method of making a, tissue repair device having a polymeric stoppermember molded around an end of a flexible cord, comprising the steps of:providing a flexible cord having a first end and a second end, the firstand second ends being flexible; providing a rod member; placing the rodmember through the first end of the cord such that at least a section ofthe rod member is contained within the end of the cord; disposing thefirst flexible end of the cord with the rod member in a die cavity;providing a prefabricated polymer tube having an inner passage;disposing the prefabricated polymer tube in the die cavity so that itsubstantially surrounds the first end of the cord and the rod member;disposing a plunger in the die cavity adjacent to the polymer tube;heating the die cavity to a temperature sufficient to effectivelycompletely melt the polymer tube, thereby producing melted polymer;moving the plunger axially in the die cavity in the direction of thefirst end of the cord and the rod, thereby forming a stopper member fromthe melted polymer about the first end of the cord and the rod member;and, and cooling the die cavity, wherein the cord, the rod and thestopper member are formed from biocompatible polymers selected from thegroup consisting of aliphatic polyesters, polyorthoesters,polyanhydrides, polycarbonates, polyurethanes, polyamides andpolyalkylene oxides.
 2. The method of claim 1, wherein the cord is in aform selected from the group consisting of braid, weave, or knit.
 3. Themethod of claim 2, wherein the cord comprises a braid and is in a formselected from the group consisting of biaxial braid, and triaxial braid.4. The method of claim 1, wherein the cord, the rod, and the stoppermember comprise biodegradable aliphatic polymers, copolymers, and blendsformed from monomers selected from the group consisting of lactic acid,lactide, glycolic acid, glycolide, epsilon-caprolactone,1,4-dioxan-2-one, and (1,3-dioxan-2-one).
 5. The method of claim 1,wherein the cord comprises biodegradable aliphatic polymers, copolymers,and blends formed from monomers selected from the group consisting oflactic acid, lactide, glycolic acid, glycolide, epsilon-caprolactone,1,4-dioxan-2-one, and (1,3-dioxan-2-one).
 6. The method of claim 1,wherein the stopper member comprises biodegradable aliphatic polymers,copolymers, and blends formed from monomers selected from the groupconsisting of lactic acid, lactide, glycolic acid, glycolide,epsilon-caprolactone, 1,4-dioxan-2-one, and (1,3-dioxan-2-one).
 7. Themethod device of claim 1, wherein the rod member comprises biodegradablealiphatic polymers, copolymers, and blends formed from monomers selectedfrom the group consisting of lactic acid, lactide, glycolic acid,glycolide, epsilon-caprolactone, 1,4-dioxan-2-one, and(1,3-dioxan-2-one).
 8. The method of claim 1, wherein the cord comprisespoly(lactic acid).
 9. The method of claim 1, wherein the rod membercomprises poly(lactic acid).
 10. The method of claim 1, wherein the cordcomprises poly(lactide-co-glycolide) in a mole ratio of 95 lactic acidto 5 glycolic acid.
 11. The method of claim 1, wherein the stoppermember comprises poly(epsilon-caprolactone-co-1,4-dioxan-2-one), in amole ratio of 95 epsilon-caprolactone to 5 1,4-dioxan-2-one.
 12. Themethod of claim 1, additionally comprising the steps of providing asecond rod member, locating the second rod member in the second end ofthe cord, providing a second polymeric tube, and molding a stoppermember about the second end and rod member.